I don't believe these compatibility based opinions are cultivated at such an early age.
If some are, the desire to fit in, or be accepted by one's peers, overrides the need to express his or her views.

Priorities are also different at that age.

Food, sleep, pass test, school crush, wank, lie to parents...

Repeat.

When we are young we don't talk about religion or any beliefs. Other things take up our time. We still can be friends with people who are religious as long as they and you don't try to constantly ram those beliefs down each others throats. There is more to life than believing in god or gods.

I do not have any friends from grade school and high school. I looked for and found my 6th grade best buddy several years ago. I have no idea what her religion or her politics are but I do know all she wants to talk about is playing gambling games on the computer and we no longer have anything in common.

I have friends from college and my work life some of which I have kept for 50 years. Some are religious, But accept me as I am. All of them are disgusted by trump.

I tried to paint a picture because that often explains things better then words. I was definitely intrested in different things as a child and a teenager. Often I was dairy caught up in a specific thing like horses dogs or boys as were the people I ran around with. As an adult, life made me move on to different things and created the requirement for me to become more serious about the world I lived in. I'm sure some of my high school friends became fundamentalists and since this is Oklahoma I'm positive many are republicans.

I hope you find a more suitable tribe than the kids you were growing up with.

Since you are posting this on an A/A site, I will guess that you're beliefs fit into that range of beliefs. And, since a Pew Research Center poll done in 2012, found that A/A's numbered, 5.7%, you are almost certainly in the minority of your probably somewhat randomly found group of H.S. friends. Depending on how many friends you are considering were in your group, you may be the only A.com/A among them.
I think that when we are at H.S. age, or younger, as long as another kid does not turn us off in some particular way, and enjoys doing the things we do, we don't usually worry about their beliefs. Yes, if someone is adamantly, vociferously, coming from a different perspective, that ought to not hold true.
I was always an atheist, and expect that none of my neighborhood, or H.S. friends, and acquaintances were. But, it never came up. I do not believe that any of my buddies ever asked me why I was had no Bar Mitzva.

When I was five, I thought I was all grown up.
When I was ten, I thought five yr olds were just dumb little kids.
When I was fifteen, I thought ten yr olds were dumb little kids; and that you weren't supposed to trust anyone over thirty.
This year, I will be sixty-five, and don't trust anyone under thirty.
Life is a life-long learning experience.

Very few HS friends are more than acquaintances 15 years later. (Also a reason people who marry young get lots of divorces). People grow/change or stay stuck, you may do so also, but probably not on the same timeline.

We don’t automatically develop opinions on religion. They develop over time. It’s no surprise that you’ve moved on.

When we are younger, we are invincible. Nothing matters but a good time and some good food and in my case, the promise that the beautiful girl you fancy will fall in love with you. I'm like you, all but a few of my friends are Christians and we are in fora where daily eproselytizing is the norm. Once in a while I step in to decry some shocking utterances. The condescension!
Well, true friendships are rare. Our multiple connections heavily influence how we view others.

We all do stupid shit when we are that young.

What was important to you in your High School days is very likely quite different than what is important to you now.

Interesting question.

As I have become more aware of the insidious properties of religion (dishonest faith (belief without evidence) asserted as truth (things based in reality that can be tested)) based (lack of logical) mindset, damage religion does to people, anti-reason virus, waste time and resources on nonsense, etc. I have become significantly less tolerant with the religious.

When I was younger (from about age 7 to early 20's) I thought religion was nothing more then a mind-fuck game adults played on their children to keep them afraid and obedient.

I reasoned, this nonsense (faith based religion (that I noticed did NOT represent reality)) is so stupid, surely no adult actually believes this BS.

In my 20's I became painfully aware adults actually believed their fairy tales. I still remember the place and time I came to that dreadful realization. My positive outcome for the advancement of civilization took a profound hit that day.

For me, close friends, I made it a point to select as friends those with superior intelligence. (Geeks, nerds etc.) For my good friends, It took them a lot longer but all close friends are now atheist. Funny, I still remember getting together with one five years after he left the state. . . his question. . . "How did you know (religions was BS)? It took me a long time but you always knew. . ." There is still one lesser friend (one of only two who live within a thousand mile radius) who is a superstitionalist but I don't waste much time with him.

As people get older they become their parents.

Only you can know if you have a true friendship.

One of my friends is a Republican who, in many ways, is the opposite of me. Gleefully calls herself a redneck. She is getting married for the fourth time. She raised her kids (in their 20s) to be lazy layabouts who break the law.

But Kami and I have fun together. With shared intensity, we riff off each other's humor and laugh about our differences.

My friends changed after I became a parent in my 30s. I met couples in Lamaze class. We had babies at the same time. We became friends and our kids played together.

Good questions, and had the same experiences… I think we ignored their core beliefs, or hadn’t bothered to ask.. In time, 3 of my closest friends all turned out to have religious beliefs, especially after children.

I suspect, in the day, we were more united by the suppression of youth than that of religion. Though I’d definitely displayed disrespect for adult authority and religion, friends never challenged me on either. As we matured, distance was likely enhanced due to religion … cuz ..we’d ‘become the adults’

Most of the people I hung out with in high school, the ones I still have contact with, are perfectly in sync with me politically. Of course, the 1960s were a politically charged decade, and we were all involved.

False dichotomy. Either or argument. Circumstances & people change. That is the constant. Get used to it.

Someone once put it to me like this, People have different burn rates, some people burn bright and some people burn low, some people are like roman candles that light up the sky for an instant and then they are gone, some people just fade away. Everyone is different and things change, people change and some people never change, what you learn over time is that you can't hang onto the past, you can only learn from it.

Same here

Yes, unfortunately. I think we all evolve over time to naturally become more conservative. I think experience and the sense of mortality sink in and accounts for much of it. I too, right now as a matter of fact, am arguing with a buddy from H.S. (Class of 91) and neither of us were ever political. I was in restaurants and watched neo-liberalism destroy us through the explosion of for profit culinary schools stacking over a 200% work force for the jobs available. That cut the salary of your average chef by more than half. I then became a cab driver and that was doing so well I thought I'd have my own restaurant in 2 years. Then Uber gave Governor Sandoval hundreds of millions of $'s and I was out another job.

I researched a lot and discovered Neo-Liberalism and how it has destroyed us. For those who don't know, Neo-Liberalism has nothing to do with Liberals or the left. It is the ideology of how a Nation State sees its place in the world and all of our government is Neo-Liberal. So is the EU and Great Britain. Runaway Capitalism with no Moral Guidelines is the best definition and would be a more apropos name. So I went left. My friend is in Finance for a large Insurance Co, in the Credit Assurance Dept. basically he makes a win out of someone else's loss. For some reason the original lender is not allowed to do that to save the deal in the first place, but I digress...He went right, far right. He discovered Fox and they drew him in. He is now a talking head for the most untruthful network that calls itself a Commentary Network whenever they get sued for Libel.

But he is heavily into politics these days and supports one side and one side only. I might have gone to the left, but I study history and our society was never better than it was from the 40's to the 70's and both Republicans and Democrats agreed on a great many things that made it that way. Until the day they didn't.
So I love him like a brother but if I am less than honest to avoid an argument, that's not a true friendship. And if all we do is argue because I reject his overtures trying to turn me into a mindless acolyte of a political party, then that's not a true friendship either. We will always be friends in the sense that we will be there for each other in a time of need, but we cannot enjoy each others company if there is always tension. So while nothing would make us not true friends, respecting my opinion just a little would make us friends in a truer sense of the word. Because I certainly respect his, even though anyone else I would call bat shit crazy.

It depends. I have a friend who is a completely different person from me, very little in common but I get along brilliantly with him. There are people who have quite a bit in common with me that I don't get along that well. It's a bit relative. In theory, it's easier to get along with people who have more in common with you but things are never that linear.

Welcome to the asylum. Enjoy your stay.

I think, when we're younger, our principles are still developing.
Think it takes some life experience to solidify who we are and what we believe.
The friends we have in our youth don't always stay such.
I know quite a few people that I was friends with when I was much younger that
I wouldn't have anything to do with now.
We are no longer of like minds.
If we ever were to begin with.

I have exactly 0 friends left from high school (unless you count FB friends). It's our political views that are different now. All my white 50sh friends are Trump supporters. In our 20s and into our 30s we never discussed politics. Probably wouldn't now if not for social media. Some posts you just can't unsee.

Yes it does happen but I am not sure that we can do anything about it. I temporarily lost two close friends , one was best man at my wedding. He went off me when I commented on the UK scout movement who objected to Non believer boy scouts. He got a lot out of the scouts but I joined the cadets instead.The other left his wife and took up with another woman who had dramatic troubles with the church. He also developed a rare form of Parkinson's leaving me with none of the intellectual challenge that he had in youth as he had to defend his new woman.

I grew up in the bible belt and I do not recall anything ever mentioned about religion or politics with friends as a youth.
I might add that I have had no contact with any of my high school friends since graduating as I immediately moved from AL to TX.

In my case, I changed and they stayed the same. I never quite fit in but could blend. As I grew and experienced life outside the confines of my hometown, I found that I didn't want to be part of the environment I was born into. I actually have very little to do with my immediate family and only know what's happening with my extended family through Facebook and Instagram.